The invention relates to mechanical bandpass filters and specifically to mechanical filters which employ bar resonators.
Mechanical bandpass filters are known in the Art, especially filters such as the longitudinal mode mechanical bandpass filter disclosed in my U.S. Pat. No. 3,983,516. The disclosed bar resonators operate in a longitudinal mode of vibration and are aligned in parallel array along the longitudinal axis in which they are rigidly joined together by at least two support rods at their aligned nodal planes and at least one coupling rod. Piezoelectric transducers affixed to the longitudinal surfaces of two resonators provide a means for mechanically driving the resonator assembly from an electrical input signal and for extracting an electrical output signal.
In an article published in the IEEE Transactions on Circuits and Systems of Volume CAS-22, No. 2, February, 1975, entitled "Crystal and Mechanical Filters" by Desmond F. Sheahan and Robert A. Johnson, there was disclosed the basic techniques used in the design of crystal and mechanical filters. Similarly, in a paper published by the IEEE Transactions on Sonics and Ultrasonics, Volume SU-21, No. 4, published in October, 1974, entitled "Mechanical Filters and Resonators" by Robert A. Johnson and Alfhart E. Guenther, there was disclosed the circuit equivalent of mechanical filters as well as the description of these circuits. In addition, the basic theory of bar resonator use in mechanical filters was disclosed.